Question 1

Which of the following best describes the sequence of major events during early embryonic development in a frog, as shown in the developmental cycle diagram?

Accepted Answer

Fertilization → Cleavage → Gastrulation → Organogenesis → Metamorphosis

Question 2

During the acrosomal reaction in sea urchin fertilization, what is the primary function of the hydrolytic enzymes released from the sperm's acrosome?

Accepted Answer

To digest the jelly coat surrounding the egg, allowing sperm to reach the egg plasma membrane

Question 3

Which mechanism is responsible for the 'slow block' to polyspermy in animal eggs, and what ion is crucial for this process?

Accepted Answer

Cortical reaction; $$\mathrm{Ca$$^{2+}$$}$$

Question 4

In mammals, what is the function of the trophoblast during early embryonic development?

Accepted Answer

It initiates implantation into the uterine lining

Question 5

Which of the following statements about cleavage is correct?

Accepted Answer

Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres without increasing the overall size of the embryo

Question 6

A researcher observes that the third cleavage in a frog embryo produces blastomeres of unequal size. What is the most likely explanation for this observation?

Accepted Answer

The distribution of yolk is uneven, with more yolk at the vegetal pole

Question 7

Which germ layer gives rise to the nervous system and epidermis in vertebrates?

Accepted Answer

Ectoderm

Question 8

During gastrulation in a sea urchin, which structure forms as a result of the invagination of cells at the vegetal pole?

Accepted Answer

Archenteron

Question 9

Which extra-embryonic membrane is primarily responsible for gas exchange in amniotes?

Accepted Answer

Chorion

Question 10

A mutation disrupts the formation of neural crest cells in a vertebrate embryo. Which of the following structures is most likely to be affected?

Accepted Answer

Parts of the skull and teeth

Question 11

Which process is defined as programmed cell death and is essential for proper development of structures such as the nervous system?

Accepted Answer

Apoptosis

Question 12

In the context of axis formation in the frog embryo, when is the anterior-posterior axis established?

Accepted Answer

During oogenesis, before fertilization

Question 13

Which of the following best describes the role of cytoplasmic determinants in early embryonic development?

Accepted Answer

They are molecules in the egg cytoplasm that influence the developmental fate of cells

Question 14

A scientist marks a group of cells in the animal pole of a frog blastula. After development, these cells are found in the epidermis. What does this experiment demonstrate?

Accepted Answer

Cell fate is influenced by position and cytoplasmic determinants

Question 15

Which of the following is an example of induction during embryonic development?

Accepted Answer

Cells in the limb bud secrete signals that influence the fate of neighboring cells

Question 16

Which axis is established in the chick embryo by gravity, and which by pH differences?

Accepted Answer

Anterior-posterior by gravity; dorsal-ventral by pH differences

Question 17

Which of the following best explains why holoblastic cleavage occurs in mammals and amphibians, but not in birds or reptiles?

Accepted Answer

Mammals and amphibians have eggs with little yolk, allowing complete division

Question 18

Which of the following is a direct result of the contraction of actin filaments at the apical end of cells during morphogenesis?

Accepted Answer

Cells become wedge-shaped, facilitating invagination

Question 19

A mutation prevents the formation of the notochord in a vertebrate embryo. Which process would be most directly affected?

Accepted Answer

Induction of the neural plate from the ectoderm

Question 20

Which of the following best describes the concept of positional information in pattern formation?

Accepted Answer

Molecular cues that inform a cell of its location relative to body axes

Animal Development: Fertilization, Cleavage, Morphogenesis, and Cell Fate Specification

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